1. Field of the Invention
The present invention relates to a polysilicon/silicide ("polycide") gate structure that includes an intermediate nitride layer that acts as a barrier for subsequently applied dopants.
2. Description of the Prior Art
In the production of CMOS integrated circuits, it has become common practice to form the gate structure as a dual-layer polysilicon/silicide ("polycide") arrangement. Tungsten silicide (WSi.sub.x) is an exemplary silicide that may be used in this process. Unfortunately, the material mismatch in the dual-layer arrangement results in forming high-angle grain boundaries and other high-diffusivity paths for later-applied dopants, such as boron, resulting in the underlying polysilicon layer becoming boron-doped, an undesired result. One solution to this problem is to include a titanium nitride barrier layer between the polysilicon and the silicide. FIG. 1 illustrates this exemplary arrangement, including a polysilicon layer 10, titanium nitride barrier layer 12 and tungsten silicide layer 14. Titanium nitride barrier layer 12 will retard dopant diffusion (shown illustratively as the downward arrows with the letter "B") at relatively low reaction temperatures (&lt;600.degree. C.). However, above this temperature the titanium nitride integrity deteriorates significantly, causing rapid diffusion of dopants into the polysilicon.